General and significant accounting policies (ASU 2018-12 Transition) (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2024		Dec. 31, 2023	Dec. 31, 2022	Dec. 31, 2021
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Reinsurance recoverable on losses and loss expenses	[1]	$ (19,777)		$ (19,952)
Reinsurance Recoverable Future Policy Benefits	[1]	(289)		(280)
Deferred policy acquisition costs		8,358		7,152
Value of business acquired		(3,223)		(3,674)	$ (3,702)	$ (235)
Goodwill		19,579	[2]	19,686	16,228
Prepaid Reinsurance Premiums		(3,378)		(3,221)
Liability for Claims and Claims Adjustment Expense		(84,004)		(80,122)	(75,747)	$ (72,330)
Unearned Premiums		(23,504)		(22,051)
Future policy benefits		16,121		13,888
Market risk benefits		607		771
Reinsurance Payable		(8,121)		(8,302)
Deferred tax liabilities		(1,584)		(1,555)
Retained earnings		(61,561)		(54,810)
Accumulated other comprehensive income (loss)		(8,644)		(6,809)
Premiums Written, Net		(51,468)		(47,361)	(41,720)
Premiums Earned, Net		(49,846)		(45,712)	(40,360)
Realized Investment Gains (Losses)		(117)		607	1,085
Market Risk Benefit, Change in Fair Value, Gain (Loss)		140		307	(80)
Policyholder Benefits and Claims Incurred, Net		(26,022)		(24,100)	(22,572)
Policy benefits		(4,714)		(3,628)	(2,314)
Policy acquisition costs		(9,102)		(8,259)	(7,339)
Other (income) expense		(1,023)		(836)	89
Income Tax Expense (Benefit)		(1,815)		(511)	(1,239)
Net income (loss)		(9,272)		(9,028)	(5,246)
Current discount rate on future policy benefits		(701)		84	1,480
Instrument-specific credit risk on market risk benefits		7		2	33
Other Comprehensive Income (Loss), Tax		(117)		(317)	965
Comprehensive income (loss)		7,658		12,376	(3,865)
Comprehensive Income (Loss), Net of Tax, Attributable to Parent		7,437		12,404	(3,865)
Net Cash Provided by (Used in) Operating Activities, Total		16,182		12,632	11,258
Net Cash Provided by (Used in) Financing Activities		(2,181)		(4,489)	(5,142)
Liability for Future Policy Benefit, Remeasurement Gain (Loss)		(2)		19	3
Equity in net income of subsidiaries and affiliates		(967)		(867)	(1)
Increase (Decrease) in Deferred Income Taxes		96		(1,124)	318
Unpaid losses and loss expenses		4,567		3,470	4,259
Unearned premiums		1,805		1,377	1,435
Future policy benefits		1,841		848	333
Accounts payable, accrued expenses, and other liabilities		342		(735)	(68)
Reinsurance recoverable		(30)		(498)	(1,737)
Increase (Decrease) in Deferred Policy Acquisition Costs		(1,429)		(1,100)	(396)
Increase (Decrease) in Other Operating Assets and Liabilities, Net		1,374		1,819	789
Net cash flows used for investing activities		(13,923)		(7,648)	(5,654)
Life Insurance [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Goodwill		4,641	[2]	4,742	1,943
Future policy benefits		14,680		12,679
Premiums Written, Net		(6,326)		(5,465)	(3,608)
Premiums Earned, Net		(6,273)		(5,398)	(3,510)
Policyholder Benefits and Claims Incurred, Net		(112)		(114)	(85)
Policy acquisition costs		(1,202)		(1,089)	(785)
Other (income) expense		(159)		(115)	(30)
Overseas General Insurance [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Goodwill		5,047	[2]	5,262	4,605
Premiums Written, Net		(13,972)		(12,575)	(11,060)
Premiums Earned, Net		(13,400)		(12,231)	(10,803)
Policyholder Benefits and Claims Incurred, Net		(6,414)		(5,643)	(4,894)
Policy acquisition costs		(3,410)		(3,113)	(2,818)
Other (income) expense		14		(25)	2
Term Life Insurance | Life Insurance [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs		469		402	324
Future policy benefits		994		931
Policy acquisition costs		(121)		(100)
Whole Life Insurance | Life Insurance [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs		870		534	392
Future policy benefits		8,862		6,917
Policy acquisition costs		(37)		(23)
Accident and Health [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Premiums Earned, Net		(6,488)		(6,233)	(4,892)
Accident and Health [Member] | Life Insurance [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs		1,681		1,301	891
Future policy benefits		4,263		4,383
Policy acquisition costs		(182)		(137)
Insurance, Other [Member] | Life Insurance [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Deferred policy acquisition costs		324		274	$ 268
Future policy benefits		561		448
Policy acquisition costs		$ (27)		$ (29)

[1] Net of valuation allowance for uncollectible reinsurance.

[2] Includes $499 million attributable to noncontrolling interests